This application claims the benefit of Korean Application No. 99-13983, filed Apr. 20, 1999, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to signal reproduction technology, and more particularly, to a circuit and method of detecting a blank component with a playback signal read from an optical disc.
2. Description of the Related Art
A recording and/or reproducing apparatus for recording and/or reproducing data with respect to an optical disc such as a compact disc (CD) or a digital versatile disc (DVD) among recording media, emits a beam from an optical source such as a laser diode onto the surface of the disc, converts the intensity of light reflected from the disc surface into an electrical signal, and reads out the data recorded on the disc. Here, the electrical signal is referred to as a radio frequency (RF) signal. The RF signal is decoded into a binary signal and the decoded binary signal is used as necessary through a demodulation process.
However, since the disc surface has various flaws or polluted by dirt, the RF signal is not always detected as a certain value having a predetermined amplitude corresponding to the size of a recording mark. Also, data to be reproduced is logically continuous, but may lie scattered physically at various portions of the disc. Here, a pickup does not always move from the inner circumference of the surface of the disc to the outer circumference thereof sequentially. At times, the pickup may jump a predetermined distance on the disc surface. The RF signal detected at the instant time when the pickup jumps has a smaller amplitude than that of normal reproduction.
A signal indicating that a current signal is abnormal in the case that the abnormal RF signal has been detected is called a blank signal. The blank signal is provided to a phase locked loop (PLL) circuit (not shown) or a binary data decoder (which is called a slice circuit), which is used to hold the phase locked loop or stop the output of the binary data temporarily.
A conventional blank detection circuit has an analog configuration as shown in FIG. 1. A first hold circuit 12 detects an upper value of an input RF signal, and a second hold circuit 14 detects a bottom value of the input RF signal. If the upper and bottom values of the input RF signal are detected, a first comparator (COMP1) 16 compares the upper value with a first threshold value (TH1) and a second comparator (COMP2) 18 compares the bottom value with a second threshold value (TH2). As a result, if the upper value is smaller than the first threshold value (TH1) in the first comparator 16 or if the bottom value is larger than the second threshold value (TH2) in the second comparator 18, a blank signal is output through a logic device 20.
In the conventional art, since the first hold circuit 12 tracking the upper value of the input signal and the second hold circuit 14 tracking the bottom value of the input signal each use an analog low-pass filter, as shown in FIG. 1, it is not possible to perform quick tracking with respect to the input signal. Although a quick tracking is performed by increasing a critical frequency of the low-pass filter, a signal band of a long-term period included in the input RF signal is trespassed, and accordingly a blank signal is not detected well. That is, if the characteristic of the low-pass filter is too sensitive, a blank signal is detected at an unwanted position, while if the low-pass filter is not sensitive enough, a blank signal is not detected at a desired position. Thus, it is difficult to accurately detect a blank signal at a defective area or a position where a normal reproduced output is not detected as in a jump operation.
To solve the above problems, it is an object of the present invention to provide a blank detection circuit implemented by a digital circuit, in which an RF signal read from a recording medium such as a disc is converted into a digital signal.
It is another object to provide a blank detection method of detecting a blank of a signal read out from a recording medium such as a disc quickly and accurately.
Additional objects and advantages of the invention will be set forth in part in the description which and, in part, will be obvious from the description, or may be learned by practice of the invention.
To accomplish the above and other objects of the present invention, there is provided a blank detection circuit for detecting a blank of a reproduced signal read from a recording medium, the blank detection circuit comprising: an edge detector which detects edges of the reproduced signal and detects an interval between the detected edges, which is an inter-edge interval; a maximum value/minimum value detector which detects an amplitude of the reproduced signal in response to the edge and provides a maximum value or a minimum value of the detected amplitude; and a determiner which determines whether the reproduced signal is the blank according to the inter-edge interval detected in the edge detector and/or the maximum value or minimum value detected in the maximum value/minimum value detector.
To accomplish the above and other objects of the present invention, there is also provided a blank detection method of detecting a blank of a reproduced signal read from a recording medium, the blank detection method comprising: detecting edges of the reproduced signal and detecting an interval between the detected edges, which is an inter-edge interval; detecting an amplitude of the reproduced signal and providing a maximum value or a minimum value of the detected amplitude; and determining whether the inter-edge interval, the maximum value and/or the minimum value meet predetermined conditions, and if met, generating a blank signal.